1. Field of the Invention
The present invention relates to devices for gross filtering of intake water needed by systems demanding a large flow of water free of large-sized debris. More particularly, the present invention relates to grates or trash racks fabricated with structural reinforcement for the strengthening of non-metallic members exposed to the water. The present invention includes a fiber-reinforced material formed in the shape of a rod as the reinforcing component of the trash rack.
2. Description of the Prior Art.
For many years, water intake systems have been filtered using trash racks made of metal, steel in particular. More recently, there has been increasing interest in the use of trash racks made substantially of non-metallic materials. The inventor of the present invention obtained U.S. Pat. No. 4,846,966 on Jul. 11, 1989 (the Pastore patent) for such an improvement in trash rack design. The advantages of using non-metallic materials are described in that patent. The disclosure made in the Pastore patent regarding the deficiencies in the prior metal trash racks, and the disclosure of the advantages of fabricating the longitudinal members of non-metallic materials, are incorporated herein by reference.
Of particular concern to the present invention is the means for reinforcing the longitudinal elements of the Pastore non-metallic trash racks. Specifically, it is noted that Pastore teaches in his preferred embodiment the use of a coaxial structure including a central core of cast thermoset plastic or steel surrounded by a cylindrical sleeve. While that design is suitable, provided the steel central core is isolated from direct contact with water, it may be more complex than required. In addition, testing conducted subsequent to the grant of that patent indicates that cast thermoset plastic alone as the reinforcing component was too brittle to withstand the various significant static and dynamic loading applied to the trash racks. As a result, cast thermoset plastic was replaced with steel rods as the core in the Pastore trash racks.
It was also discovered that the non-metallic spacers used to space the longitudinal members of the rack apart were sufficient to isolate the steel reinforcing rod from water. It was determined that steel could be used to increase the structural integrity of the non-metallic racks without express concern as to ice and marine growth--provided the steel was not directly contacted by the water. However, as noted in the Pastore patent, steel has a much higher density than non-metallic materials. Therefore, although the Pastore trash rack is formed substantially of non-metallic materials and is therefore of much lighter weight than equivalently-sized prior metal trash racks, the continuing use of steel makes these racks heavier than they otherwise may be. Given the sizes of the trash racks--they may span rivers several hundred yards wide and wider--it would be advantageous to reduce their weight, but without detrimental effect on their usefulness.
A concern that has been discovered in using steel reinforcing rods is that steel does not have the "give" or flexibility to bounce back under high impact conditions. That is, when significantly-sized debris--such as a log or a dense pack of frazil ice--contacts the rack, it forces the rack to bend. Upon removal of that load, the rack may well remain contorted because the bent steel used to reinforce the longitudinal members will not rebound. Although steel has some small degree of elasticity, it is not sufficiently elastic, or flexible, to recover from some of the types of loads experienced by trash racks. Therefore, the use of steel rods, while aiding to strengthen the substantially non-metallic trash racks, may result in undesirable failure under some conditions. The distortion that may occur would require premature replacement or significant maintenance activities.
What is needed is a non-metallic trash rack that filters coarse debris at the intakes of power generating systems and other systems requiring large amounts of water. What is also needed is a non-metallic trash rack that is as light weight as possible. Further, what is needed is a non-metallic trash rack that will recover to substantially its original shape upon removal of a load of the type commonly associated with trash racks for large volume water intakes. Still further, what is needed is such a trash rack that will not fracture upon being impacted by debris or ice of the type associated with such systems.